I suppose "largest" depends on how you quantify it. The longest reported nonvenomous snake was a reticulated python that topped out at 33 feet (10 meters) long. The heaviest / bulkiest snake was a green anaconda that was reported to be 29 feet (8.8 meters) long and around 500 lbs. (227 kg). Those reports may or may not be accurate. Without anesthetizing the snake, laying it out and getting precise lengths and weights those claims can be dubious. A lot of people overestimate the length and weight of snakes they encounter and even photographs can be misleading.

The longest species of venomous snake is the king cobra at up to 19 feet (6 meters) and the heaviest is the Gaboon viper (up to 44 lbs. or 20 kg). The Gaboon viper also holds the record for longest fangs and highest volume of venom delivered in a bite.